please snap picture from ENGINE Bay of vehicle for such routing .. if it is how u posted it seems something seriously wrong. bottom goes to water pump inlet, - top one is to complete water circulation when car is hot & thermostat is open for coolant flow. if your mechanic have done some by-pass as in post, how coolant will flow to maintain engine temp?

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This is the current situation. Line in Red color is showing the bypass pipe (CNG kit was in between before)

First this diagram is wrong. Put the T-valve inside engine not away from it.

Second if you are describing it right - the red line - then you radiator is not bypassed its actually your heater core that is bypassed.
Its a bullcrap done by mechanics in summer season - when heater is not being used - to avoid any hot air leaking into cold air of AC and effect its cooling.
Doing this be ready to get your heater core repaired the next time you put it back in circulation in winter season. Since it would be leaking.

First this diagram is wrong. Put the T-valve inside engine not away from it.

Second if you are describing it right - the red line - then you radiator is not bypassed its actually your heater core that is bypassed.
Its a bullcrap done by mechanics in summer season - when heater is not being used - to avoid any hot air leaking into cold air of AC and effect its cooling.
Doing this be ready to get your heater core repaired the next time you put it back in circulation in winter season. Since it would be leaking.

Dear, i made a rough diagram only which i could see easily. definitely T-valve is attached with the engine. Heater core is bypassed but indirectly radiator is also bypassed (i mean top and bottom pipes are joined near heater pipes) but i used heater in same situation in last winter. Heater was working fine.